1. Field of the Invention
The present invention relates generally to the dyeing of textiles and, more particularly, to a liquid alkali for use in fiber reactive dyeing of cotton and cotton blended fabrics.
2. Description of the Prior Art
Fiber reactive dyes were first introduced in 1956. Since that time they have become a dominant factor in dyeing cotton, regenerated cellulose and blends. These dyes can also be used to dye acrylics, nylon, silk, and wool and blends of these fibers. Fiber reactive dyes are easy to apply and produce brilliant shades, fastness, penetration and leveling.
Fiber reactive dyes are anionic in nature and react chemically with the fiber. The dyes include a chromophore to give color to the dye and a reactive group to form a chemical bond with the fiber. There may also be a substitutent or solubilizing group which provides additional dyeing characteristics such as solubility, substantivity, migration, washing off, etc. Fiber reactive dyes react in the presence of alkali to form a strong covalent chemical bond between a carbon atom of the dye molecule and an oxygen atom of the hydroxyl group in the cellulose. This step is called "fixing".
The following alkalis have all been used to obtain the "fix" of different classes of reactive dyes to cellulose fibers:
______________________________________ Sodium Hydroxide Potassium Hydroxide Trisodium Phosphate Sodium Tripolyphosphate Sodium Carbonate Sodium Bicarbonate Sodium Silicate ______________________________________
However, no single alkali system has worked on all classes of reactive dyes due to the differences in the rate of hydrolysis of each dye. Of all the alkali systems, the liquid phosphate system described in U.S. Pat. No. 4,555,348, issued to Moran, and sold under tradename Alkaflo by Sybron Chemicals of Birmingham, N.J., works almost universally. But Alkaflo is high in phosphorus which can contribute to environmental problems.
Another commercial liquid alkali is sold under the tradename Burco NP-Q Salt and is available from Burlington Chemical Co., Burlington, N.C. This product is based on a mixture of sodium hydroxide, potassium hydroxide, soda ash, citrate, acrylate salt. The resulting neutralization/buffer curve is similar to the phosphorus-based Alkaflo. The problem with both NP-Q Salt and Alkaflo is that hydrolysis is still too quick when using Trichlor Pyrimidine, Difluorchlor Pyrimidine or Dichlorchinoxaline dyes (sold under the tradename "Levafix" and available from ICI America, Wilmington, Del.). While these alkalis are suitable for sulfatoethysulfone or chlortriazine dyes, they are too "hot" for the Levafix-type colorants.
Another alkali which has been used on and off, as discussed above, is sodium carbonate. In difficult dyeing situations, i.e., matching shades with reactive dyes of differing reactivities, sodium carbonate demonstrates the best overall dyeing performance because of high Total Alkalinity and good buffering. The problem with sodium carbonate is that it takes 20% on weight of bath (OWB) to fix the dye. Unfortunately, the maximum g/L total solubility of sodium carbonate (approximately 25%) limits the concentration of the liquid alkali that can be produced. In addition, using the alkali as a powder is not feasible in modern dyeing equipment.
The problem with using a solution of sodium carbonate is further complicated due to changes in dyeing that occur when adding large amounts of liquid to dyebaths, i.e. changes in liquor ratio or fabric to water ratio. In essence, when large volumes of liquid are added to reactive dyebaths, a dilution occurs which changes the concentration of the dye in contact with the fiber. Therefore, it is advantageous to add as low a volume of alkali as possible.
Assuming a sufficiently concentrated solution could be prepared, the best product would be a liquid alkali with a high enough Total Alkalinity to achieve the reaction between the dye and fiber but sufficiently buffered to achieve this reaction slowly so that the dye fixes in a level uniform fashion. The difference between the Active and Total Alkalinities is especially important, the greater the differential, the better the ultimate performance.
However, if the reaction mixture is too "hot" or alkaline, such as is seen with pure sodium hydroxide, the sensitive-type reactive dyes will hydrolyze with the water in the dyebath and form a nonreactive pigment that has no effect on the fabric color. Furthermore, as fashions have changed, the need to mix reactive dyes of different chemistries in the same shade and the necessity of developing a universal alkali system for cold pad batch dyeing that does not contain silicates or phosphorus has become more important.
Thus, there remains a need for a liquid, phosphorus and silicate-free, alkali for use in fiber reactive dyeing of cotton and cotton blended fabrics which has a buffer curve similar to sodium carbonate but with the clean dyeing properties of a phosphorus-based system such as Alkaflo.